1. Field of the Invention
This invention relates to a method for transmitting record control signals to a recording circuit of a magnetic recording apparatus, in which the recording circuit provided with an amplifier connected to a magnetic head is provided on the side of a rotary head drum, and a record control circuit for controlling the operation of the recording circuit. The present invention may be applied to, for example, a video tape recorder provided with a rotary head drum.
2. Prior Art
In some of the magnetic recording/reproducing apparatus, such as a video tape recorder, provided with a rotary head drum, a recording amplifier and a reproducing amplifier or the like are provided within the rotary head drum in consideration that otherwise the frequency response or transmission efficiency by a rotary transformer provided between the magnetic head provided in the rotary head drum and the recording processing or reproducing processing circuit on the side of a fixed substrate may be lowered. In the magnetic recording/reproducing apparatus in which the recording amplifier, the reproducing amplifier and the like are provided in the rotary head drum, various control signals are transmitted with the aid of, for example, a slip ring device or an optical transmission system for performing switching control of the recording head within the rotary head drum, on-off control of the recording current and switching control of the reproducing head from outside the rotary head drum.
By way of illustration, FIG. 1 shows a recording system for a four channel digital video tape recorder in which a recording circuit 103 provided with four channel recording amplifiers (102A), (102B), (102C) and (102D) is provided on the rotary head drum side. These recording amplifiers amplify recording signals REC.A.sub.CH DATA, REC.B.sub.CH DATA, REC. C.sub.CH DATA and REC.D.sub.CH DATA for respective channels, transmitted from outside via a rotary transformer 100 as four channel recording signals REC.DATA, and supply the amplified signals to recording heads 101A, 101B, 101C and 101D for respective channels. In such recording system, there is provided a four-channel digital to analog (D/A) converter 104 in a recording circuit 103 on the rotary head drum side for forming gain control data CNT.A.sub.CH, CNT.B.sub.CH, CNT.C.sub.CH and CNT.D.sub.CH to perform channel-wise gain control of the recording amplifiers 102A, 102B, 102C and 102D. In this recording system, the gain control data CNT.A.sub.CH, CNT.B.sub.CH, CNT.C.sub.CH and CNT.D.sub.CH as well as data indicated by serial data D/A DATA, sync clock D/A CK and control signals D/A ENABLE therefor are transmitted from outside the rotary head drum to the rotary head drum side by way of transmission lines 105, 106, 107 provided in a slip ring device 108 to activate the D/A converter 104 on the basis of the sync clocks D/A CK and control signals D/A ENABLE to form the gain control data CNT.A.sub.CH, CNT.B.sub.CH, CNT.C.sub.CH and CNT.D.sub.CH from the data D/A DATA at the D/A converter 104 to perform gain control of each of the recording amplifiers 102A, 102B, 102C and 102D to effect recording control for each of the respective channels.
In general, in a serial data transmission system, when serial data are received at the receiving side by D-flipflop or shift register, there are required clocks synchronized with these serial data or control signals indicating the start and stop points for the serial data. Thus the transmission line 105 for the serial data D/A DATA, the transmission line 106 for the sync clocks D/A CK and the transmission line 107 for the control signals D/A ENABLE are provided in parallel, as in the above mentioned recording system.
In a so-called self-clock type transmission system in which clock signals are superimposed on the transmitted serial data, as shown in FIG. 2, a clock generator 110 by a phase locked loop (PLL) made up of a phase comparator 111 and a voltage controlled oscillator 112 is provided at the receiving side and the data edge phase of the serial data DATA transmitted from the transmitting side over a transmission line 120 is compared with the oscillating phase of the voltage controlled oscillator 112 at the phase comparator 111 to control the oscillating frequency of the voltage controlled oscillator 112 to form the sync clocks CK for the serial data DATA at the clock generator 110. These sync clocks CK are supplied to a clock input terminal of the D-flipflop 115 on the receiving side, while the serial data DATA are supplied to a data input terminal of the D-flipflop 115.
Heretofore, in a magnetic recording apparatus in which a recording circuit provided with an amplifier connected to the magnetic head is provided on the rotary head drum side, when the record control signals controlling the recording circuit are indicated by the serial data and data enable signals indicating data start and data end points of the serial data and these serial data and data enable signals are serially transmitted simultaneously with the sync clocks therefore, the serial data, data enable signals and the sync clocks are transmitted from outside the rotary head drum towards the rotary head drum over respective separate transmission lines, so that, with the use of ship ring devices as a transmission line, it is necessary to provide multistage slip ring devices, which in turn prove to be a hindrance to the reduction in size of the magnetic recording apparatus. The multistage slip ring devices are also inconvenient in that the torque of the drum motor adapted to cause rotation of the rotary head drum is thereby affected adversely and in that the S/N ratio is also lowered due to occasionally produced shaft oscillations.
Although the number of stages of the slip ring devices may be reduced by transmitting the serial data indicating the record control signals simultaneously with the sync clocks superimposed thereon, it is necessary in this case to provide the PLL type clock generator as described above on the receiving or rotary head drum side, so that a rather wide space need be set aside for this clock generator.